Modern motor vehicles are frequently equipped with vehicle control systems. Examples that can be cited in this connection include start-stop systems, by means of which, for example, during a stop at traffic lights or in the case of a traffic jam, fuel can be saved by switching off a combustion engine of the motor vehicle. In the case of motor vehicles with manual transmission, the start-stop system switches off the combustion engine of the motor vehicle when the neutral gear is engaged, as long as the driver does not actuate the clutch pedal. When the clutch pedal is again actuated, the combustion engine is automatically restarted. In the case of motor vehicles which are equipped with automatic transmission and a start-stop system, the engine is switched off, for example, when the driver actuates the foot brake for a specific time period when the motor vehicle is stationary. Particularly in the case of motor vehicles which are equipped with start-stop systems of this type, it is important to recognize in a reliable manner that the driver has left the motor vehicle. Otherwise, the motor vehicle could be mistakenly restarted, even though the driver is no longer located in the vehicle passenger compartment.
“Adaptive Cruise Control” (ACC) systems can be cited as further vehicle control systems that are used in motor vehicles. In the case of these adaptive cruise control systems also, it is important to recognize in a reliable manner that the driver has left the motor vehicle.
The door contact switches of a driver's door of the motor vehicle are frequently used to detect whether the driver has left the motor vehicle. These door contact switches are normally disposed in a door lock and are designed in such a way that they are actuated by the opening or closing of the driver's door and thus generate door contact signals indicating whether the driver's door is opened or closed.
In order to be able to reliably recognize a door opening or door closure, two door contact switches that are independent from one another are normally provided, so that, if one of the two door contact switches fails, the other, still operational, door contact switch can provide a corresponding door contact signal and redundancy is thus provided. The disadvantage of using two redundant door contact switches is that additional component costs are thereby incurred.
A method is known from DE 10 2010 052 582 A1 for recognizing an opened door of a motor vehicle, said method working with only one door contact switch. In this method, a counter is set following an activation of an electrically driven door lock motor, said counter being able to monitor the time duration after the door lock motor has been activated. If no door contact signal of the door contact switch indicating that the door has been opened has been received within a predefined time duration, the “door contact fault” status is established and the basic state is again selected, in which monitoring is carried out in order to determine whether the door lock motor has been activated by a user.
If the motor vehicle has been started several times without corresponding door contact signals having previously been detected, it is assumed in this method that the door contact switch has a defect. For example, an error is detected if the driver enters the motor vehicle via the passenger door and starts the drive unit, since no door contact signal was detected before the drive unit was started.